Bail out and try to force a reconnect if our broker's consumer is nulled

Still need to explore how we're getting into this state, but this is a start to
handling that scenario more gracefully

References #130

src/main/groovy/com/github/lookout/verspaetung/KafkaPoller.groovy

@@ -115,6 +115,14 @@ class KafkaPoller extends Thread {
 
     Long latestFromLeader(Integer leaderId, String topic, Integer partition) {
         SimpleConsumer consumer = this.brokerConsumerMap[leaderId]
+
+        /* If we don't have a proper SimpleConsumer instance (e.g. null) then
+         * we should reconnect on our next time around
+         */
+        if (!(consumer instanceof SimpleConsumer)) {
+            this.shouldReconnect = true
+            return 0
+        }
         TopicAndPartition topicAndPart = new TopicAndPartition(topic, partition)
         /* XXX: A zero clientId into this method might not be right */
         return consumer.earliestOrLatestOffset(topicAndPart, -1, 0)
@@ -128,6 +136,7 @@ class KafkaPoller extends Thread {
      * Blocking reconnect to the Kafka brokers
      */
     void reconnect() {
+        disconnectConsumers()
         logger.info("Creating SimpleConsumer connections for brokers")
         this.brokers.each { Broker b ->
             SimpleConsumer consumer = new SimpleConsumer(b.host,
@@ -138,7 +147,7 @@ class KafkaPoller extends Thread {
             consumer.connect()
             this.brokerConsumerMap[b.id] = consumer
         }
-        this.shouldReconnect =false
+        this.shouldReconnect = false
     }
 
     /**
@@ -146,8 +155,13 @@ class KafkaPoller extends Thread {
      */
     void die() {
         this.keepRunning = false
+        disconnectConsumers()
+    }
+
+    private void disconnectConsumers() {
         this.brokerConsumerMap.each { Integer brokerId, SimpleConsumer client ->
-            client.disconnect()
+            logger.info("Disconnecting ${client}")
+            client?.disconnect()
         }
     }